removing air from gypsum casting

[dawie]

where can i find plans to build a shaker to remove air bubbles from gypsum moulds of hands and feet? currently we gently tap the mold to try and remove the bubbles durring casting.

[Geof]

You need a vibrator rather than a shaker I think, and here is a suggestion that may sound a bit loopy but it is based on the vibrating probes used to get air bubbles out of concrete. Get an electric toothbrush, there are various types available and one I have just vibrates like crazy. Hold it against the outside of the mold or trim all the bristles off the brush and use it as a vibrating stirrer.

[DMF_TomB]

i have thought about using a vibrating electric dremel engraver. if the point was removed it could be attached to the mold. for something big some sort of vibrator like the use for concrete may be needed

also i have heard painting a thinned liquid soap on mold helps the bubbles move faster, as something they are stuck

when mixing try to mix by not getting the bubbles in the first place.

let mold set in a pressure pot. for vacuum degassing and as a pressure pot try a pressure cooker like you can get at Walmart for about $20. they come with a pressure relief so if air charged they will vent or limit air pressure to prevent blowing up. obviously use as little as possible air pressure for safety.

[JerryFlyGuy]

Two other possible solutions would be to use a vacuum to de-gas the mix prior to pouring it. The second is to take a cheapo hammer drill [$25 from Peavey Mart [Harbour Freight?]] and using a cut off chunk of 3/8" rod [or similar] in the chuck and using this to 'hammer drill' the side of the mold. Worked like a charm when I poured the refractory for my furnace.

Fwiw

J